Surface hardening metal areas of limited size



June 26, 1945.

P. A. ABE ET AL SURFACE HARDENING METAL AREAS OF LIMITED SIZE Filed Feb. 5, 1941 OXlDlZED PARTICLES BEFUQE MOLDING INVENTORS Pulusm R ABE HERBERT ".BROVJN JFIlEr-r E III.

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MELVIN KCRDSBY AT l'DQhEYS Patented June 2a, 1945 2.878.800 SURFACE mnnlmma METAL Anus or LIMITED SIZE Philber A. Abe, Shiney, and Herbert H. m and Melvin A. Crosby, Dayton, Ohio, alsignors to The Monarch a corporation of Ohio e Tool 00., Sidney, Ohio,

Application February 5, 1941, Serial No. 377.528

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The present invention relates to the hardening of metals, and more particularly to the surface hardening of or drawing temper from metal surfaces of limited area.

It has been customary to heat metalsurfaces for hardening purposes by means of a gas flame. and when the proper temperature has been reached to quench the heated surface. The gas is usually oxygen acetylene at high pressure requiring tight connections, swivel Joints, etc. which restrict the portability of the apparatus and the maneuvering of the heating unit.

When it is desired to surface harden only a limited portion of a metal member, it has been the practice to draw the gas jet downward to a fine opening,'but this operation introduces back pressure within the conduits and at the Joints, thus increasing the tendency for leakage. In addition, even though the gas flame is drawn down to a needle-like point. in order severely to localize its heating effects, the flame tends to spread on striking the metal surface, due to the pressure of the gas. so that the metal surface is heated considerably beyond the zone which is to be surface hardened.

The primary object of the present invention is to provide an improved method and apparatus for heating surfaces of limited area of a metal member to a surface-hardening temperature.

Another object is to provide an apparatus which eliminates the necessity for gas heating or any other form of external heating, and yet can be applied to a limited area of a metal member, either for surface hardening or drawing the temper effects.

These objects are carried out. in brief, by permeating a metal surface by high frequency magnetic induction lines of force in concentrated form, and obtained b a focusing effect from a high frequency induction coil. In case the sur-- face is to be hardened, the heated portion is immediately quenched, or otherwise chilled after {the surface has reach ed a hardening temperaure.

The invention will be better understood when the following description is perused in connection with the accompanying drawing.

In the drawing:

Figure 1 is a sectional view of the improved surface hardening unit in position for hardening the metal immediately adjacent a tapped hole.

" -Figure 2 is a sectional view of a modified form of the unitad apted to surfaceharden the outer portion of a lathe center.

focusing coil with a conical shaped core for accentuating the focusing eiiect.

Figure 4 illustrates the facility with which the surface hardening unit can be moved about the periphery of a cam. Figure5isahighly magniiiedview of amass of oxidized metal particles before being molded and sintered to shape for use as a focusing core.

Figure 8 is a longitudinal sectional view taken through the handle 5 in Figure l in order to show atypical valve construction which can be mechanically controlled in accordance with the principles of the present invention.

Referring more particularly to Figure 1, reference numeral i designates a solenoid having a central opening 2, the exterior surface of which is tapered from the top to the bottom to constitutel'in general, a conical configuration. The opening 2 preferably has the same diameter throughout its length. The individual turns of the coil or solenoid are preferably of bare wire, separated from one another as indicated and taped so asto provide rigidity of construction. The upper layer of the coil is secured in any suitable manner to a heavy plate I of insulating material such as hard rubber, Bakelite or Celluloid. The latter may be integrally secured to a rod 4 which, in turn, leads to a handle 5, all constituted of the same material. The plate 3 has a configuration the same as the coil i except that it extends somewhat beyond the outer diameter Figure 3 shows the use of a highfrequency of the coil in order to provide a support for condlllt of insulating tubing which immediately surrounds the upper turns of the coil and is secured-to the plate I in any suitable mannenfor example, by means of the bolts I.

At the approximate center of the circular plate 3 there is an opening which receives one end 8 of the coil i, terminating in a terminal a to which a wire it is connected. The other end of the coil is indicated at H, and is provided with a terminal I! to which a wire it is connected. The wires i0, II are heavily insulated, as indicated at it, and are connected to a source of high frequency currents (not shown) preferably of relatively high voltage. The windings of the coil i may, if desired, also carry insulation of suitable character depending on the voltage applied to the terminals 8, i2 "and the temperature to which the coil is subjected. A convenient source of high frequency currents may comprise a spark gap oscillator or a Boulsen arc oscillator; also a phanotron or thyratron (electrostatically controlled are discharge rectifier) oscillator; high frequency mechanical alternator-s (of the Alexanderson type) ora Tesla oscillatory cun'ent circuit. All of these forms of oscillators are well known in the;art and are characterized by a relatively high frequency output at considerable current loads, together with any desired high or low voltage. Instead of employing an original source of high frequency currents, frequency changers such-as rotary converters in cascade, frequency doublers or triplers may, on occasion, he used to advantage. The preferred frequency will lie between 10,000 to 100,000 cycles per second, depending on the character, shape and thickness of the metal being treated, and in some cases this frequency may reach as high as 500,000 cycles per second in case the current drain is not considerable.

The high frequency currents in passing through the wire I3 to the coil I are interrupted by a switch, indicated at I5, which may be contained within the handle 5 and molded therein in case the handle is constituted of moldable material. The operation of the switch may be conveniently controlled by a lever I6, pivoted at I! and terminating in a button I8, which is so positioned as to be readily depressed by the thumb of the operator grasping the handle 5. Thus by depressing the button I8, thecircuit through the wire I3 is completed and high frequency voltage is applied to the opposite ends of the coil I. The tubing 8 may take the form of a toroid, closed at one end and at the other end communicating with a vertical pipe I 9 which extends up into the plate 3 and connects with. a horizontal bore 20 which extends along the axis of the rod 4 and the handle 5. A pipe 2| communicates with the opening 20 at one end, and at the other end is connected to a source of cool or refrigerated water, or other chilling fluid.

There is provided a valve within the handle 5 for controlling the water flowing through the bore 20, this valvebeing operated by a hand grip lever 22, pivoted at 23. The actuating rod which transfers the movement of the lever 22 to the interior valve is indicated at 24 a suitable type of valve has been shown in cross-section in Figure 6 and it will be noted that as a lever 22 is depressed. the valve is opened to permit passageway through the handle. The tubing 6 is provided throughout its length with apertures, indicated at 25, through which water or other fluid can be ejected from the circular pipe 6 when the lever 22 is pulled upwardly to open the valve in the bore 20. The position of these openings with respect to the coil I, and with respect to one another, is such as to provide a continuous curtain of water where it strikes the upper surface of the metal member 26 to be surface hardened, the curtain being drawn down to a tapered configuration corretapered or focused shape so that as the field extends itself slightly beyond the lower end of the coil much of the field will actually penetrate an annular area immediately surrounding the threads, and even as far as the lower surface of the plate 26.

The magnetic lines of force which are induced in the metal at the threads 21 cause high frequency currents to be set up in the metal, and these currents constitute independent sources of heat to a depth dependent on the depth to which the magnetic lines of force have penetrated and the strength of the magnetic lines of force. Thus by presenting the conical shaped solenoid I to the tapped hole I2 the threads may be heated to a surface-hardening temperature, and upon reaching this temperature pressure on the button I8 is removed to open-circuit the coil I, and while the threads are still at the high temperature the lever 22 is depressed by gripping the handle 5, which will cause cooling fluid to flow through the bore 20 and through the toroid 6, the openings 25, and thus to be projected against the spending to the outside shape of the solenoid I.

The use. of the improved surface hardening'unit has been illustrated in Figure 1 in connection with a tapped hole 21 formed in the plate of the metal member 26.

It is sometimes desired, in the case of a tapped hole, to harden only the metal which immediately lines of force are induced into the surface of the metal immediately adjacent the threads. Due to the tapered or conical configuration of the coil and the tendency of the magnetic field to hug the outside surface of the coil, this field takes on a heated threads to instantly quench them. Thus surface hardening effects are produced at the threaded surface. These effects usually extend for a depth just below the depth of the thread, which is approximately 15;". This depth may be controlled either'by manually moving the coil I to such a position with respect to the plate 3 as to heat the threads to a predetermined temperature, or by controlling the amount of current passing through the turns of the coil by suitably positioned rheostats in the electric supply circuit.

' The most convenient way of producing the proper surface-hardening temperature of the threads is to manipulate the unit as a whole and observe the color of the heated metal as the coil is moved to and fro by gripping the handle 5. An experienced operator can readily determine when the threads have reached the proper surface-hardening temperature.

In Figure 2 there is shown the adaptation of the improved high frequency surface hardening unit to a metal object having a projecting tapered surface such as a lathe center. The metal object is indicated at 28, and as shown terminates at its upper end in a round conical portion indicated at 29. The high frequency coil shown at 30 isformed as a solenoid having a straight out- Side diameter, but the interior is provided with a conical configuration to match that of the lathe center. The magnetic field generated at the coil is indicated by the dot-dash lines 3 I, and it will be noted that the field penetrates the lathe center only for a, limited distance and extends in a parallel direction to the conical surface. Consequently the coil, on being supplied with high frequency currents, tends to heat only the outer surface of the conical portion up to surface-hardening temperatures, leaving the interior of the lathe center at a much lower temperature. As in the case of Figure 1, the high frequency currents aresupplied to the coil through the wires 8, II, and

the coil is secured to the plate 3' in any suitable and well known manner.

The plate 3 is provided with a bore 32, and one of the walls at the center contains a number of apertures 33 directly above the apex of the l he center, so that immediately after heating the latter to a-surface-hardening temperature the cooling fluid can be ejected at the openings 33 and controlled by a suitablelever at the handle 5 (Figure 1).

the coil 30 as cool as possible, the wire is made In order to maintain the turns of of copper tubing with passageway 8| extending throughout the entire length of the coil, and water or other cooling medium may be forced through the coil at the conduits 35, 36 from a' frequency coil in connection with the case hardening of the metal immediately surrounding the tapered hole indicated at 31 in the plate 38. v The ends of the coil 39 are given a tapered configuration in order to provide a magnetic field, which in general, conforms to the shape of the coil and takes on a focused shape as indicated by the dotdash lines 40. In order to extend the focused field into the tapered opening there may be provided a magnetic core I, which has a straight cylindrical portion terminating at the bottom in a tapered portion 42 which conforms substantially to the taper of the opening 31. The core is preferablyfabricated of sintered magnetic particles which are molded to the proper shape. and then heated to a sintering temperature. These particles are preferably insulated from one another in order to reduce eddy current loss and thus to prevent the core from becoming excessively heated when high frequency currents are passed through the coil 39. It may be convenient to provide each particle with a heavy oxide layer, as for example, by passin heated iron particles through an oxidizing atmosphere prior to the sintering step.

The presence of the oxide layer is indicated in Figure 5 by the double lines 13. It will be noted that each particle is insulated from currents flowing in any direction. The presence 01' the core ll in the coil is to cause a concentration of the magnetic held at a position directly opposite the tapered opening 31 so that the metal immediately surrounding the opening and to a depth preferably of is heated to a surface-hardening temperature when high frequency currents are caused to flow through the coil.

In order to quench theheated surface a conduit II is provided which communicates with a central passageway 45 formed in the core. A plurality of openings 46 extend from the passageway l5 outwardly through the tapered portion of the core and directly opposite the tapered hole. Consequently, immediately after heating the metal surface to a surface-hardening temperature, a cooling fluid can be caused to flow through the conduit 44 and to be squirted as 'jets against the surface of the tapered hole. As in the case of the previous figures, the application of the high frequency currents and cooling medium can be controlled in any suitable manner from the handle 5 of the unit. It is apparent that the core ll may be molded prior to the sin-- tering stage to give it the proper shape and to provide for the passageway 45. The openings 46 can be readily drilled through the core after it has been sintered.

Figure 4 illustrates the use of the hand ope ated unit for surface hardening the bearing surface of a cam 41. In this figure the high frequency coil is indicated at 48. and has a tapered configuration to obtain a strong focusin action and to constrain the magnetic lines of force to a diameter at the smaller end of the coil not much greater than the thickness of the cam. Consequently, practically all of the available flux is caused to induce heating currents at the surface of the cam. The coil is secured to the plate 3 for manipulation purposes, and surrounding the coil there is a circular conduit 49 of toroidal form and carrying a cooling fluid. The fluid may be released from the conduit through the openings 50, which are so positioned as to provide a conical sheet of fluid, the apex of which extends toward the heated surface of the cam. Thu immediate quenching of the cam surface is obtained to provide surface hardening effects. It is apparent that'the surface hardening unit can be moved around the surface of the cam as fast as the successive area have been heated and quenched. The focusing effect of the coil is such as to precludeheating the cam shaft 5i to an excessive temperature, or any portion of the cam other than its outer surface.

It will be understood that it is desired to comprehend within this invention such modifications as come within the scope of the claims and the invention.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A hand-operated surface hardening unit comprising a plate of insulating material secured to a handle which serves as a grip, a high frequency coil having a conical configuration secured to said plate a cooling fluid-containing conduit and surrounding said coil, said handle being adapted to support a combined electrical switch and fluid-controlling valve in order to cause high frequency currents to p ss through the coil and at a predetermined moment to open the high frequency circuit and to cause cooling fluid to pass through said conduit, said conduit having a series of apertures directed toward the periphery of the outer windings of the coil whereby fluid is directed to follow closely the outer periphery of the coil and serves to cool the coil by convection and whereby when the smaller end of the coil is presented to a metal surface the latter is heated to a surface hardening temperature and immediately thereafter quenched in order to produce surface hardening effects.

2. A case hardening unit comprising a conical shaped high frequency heating coil secured at its large diameter to a support and permitting the small diameter end of the coil to be presented to the surface to be heated when high frequency currents are passed through the coil, a fluid containing conduit surrounding said coil and secured to said support, said conduit being provided with a series of apertures at points on said conduit in-. 

